POS0823 KL-6 IN ANCA-ASSOCIATED VASCULITIS PATIENTS WITH AND WITHOUT ILD: A MACHINE LEARNING APPROACH
Authors: E. Conticini, M. D’alessandro, L. Bergantini, D. Castillo, P. Falsetti, P. Cameli, E. Bargagli, L. Cantarini, B. Frediani
Journal: Annals of the Rheumatic Diseases (2022)

Background ANCA-associated vasculitis (AAV) are small vessel vasculitis which may variously affect upper and lower respiratory tract. Patients with microscopic polyangiitis (MPA) and, less commonly, granulomatosis with polyangiitis (GPA), especially those who are ANCA-MPO-positive, may suffer from interstitial lung disease (ILD), which is associated with high morbidity and mortality as it is often underdiagnosed and responds poorly to conventional treatments Objectives In this study, we aimed to assess whether Krebs von den Lungen-6 (KL-6), a marker of fibrotic ILD, may be useful for distinguishing AAV patients with ILD from those without ILD, and whether its changes over time are correlated with disease activity. Methods We enrolled all consecutive patients evaluated in the period December 2020 - November 2021. Inclusion criteria were a diagnosis of GPA or MPA, active disease, and eligibility for Rituximab treatment according to EULAR recommendations. All patients underwent concomitant rheumatological and pneumological evaluation, lung function tests, routine blood tests, autoimmunity evaluation and KL-6 assay. Current and previous treatments, Birmingham vasculitis score (BVAS) and vasculitis damage index were also recorded. Results A total of 13 patients (Table 1) were enrolled. One was excluded due to a concomitant diagnosis of lung cancer. Higher serum KL-6 were in AAV-ILD compared with those without ILD (972.8±398.5 vs 305.4±93.9, p=0.0040). Area under the Receiver Operating Characteristics curve showed 100% of the diagnostic performance of KL-6 for identifying the ILD involvement (accuracy 91.7%) and the best cutoff value of 368 U/mL (Sensitivity 100% and specificity 87.5%). The decision-tree model showed a 33% improvement in class purity using a cut-off value of 513 U/mL to distinguish AAV patients with and without ILD (Figure 1). Stratifying AAV patients as MPA and GPA with and without ILD considering T0 and T1 KL-6, the model obtained an improvement of 40% for classifying GPA non-ILD with a T0 serum KL-6 cut-off value of 513 U/mL and a T1 KL-6 cut-off of 301 U/mL. A direct correlation was found between serum T0 KL-6 and T0 BVAS (r=0.578, p=0.044). Table 1. Patients’ features Sex/age Diagnosis Length of disease * (months) Organs involved Type of lung involvement T0 KL6 levels T0 BVAS T0 VDI T1 KL6 levels T1 BVAS T1 VDI F/83 MPA 28 Lung, kidney, PNS ILD, alveolar hemorrhage 625 8 7 325 0 7 M/48 GPA 1 Lung, kidney, nose, eye Nodules 352 18 0 279 2 0 F/55 GPA 252 Lung, skin Nodules 401 15 3 602 3 3 F/38 MPA 1 Skin - 347 6 0 - - - F/74 MPA 180 Kidney, PNS - 368 11 5 414 0 5 M/77 MPA 8 Lung, kidney, PNS, skin ILD, alveolar hemorrhage 982 24 1 - - - F/49 GPA 60 Nose, eye - 122 6 2 116 0 2 M/60 MPA 40 Skin, PNS - 205 9 1 - - - F/39 GPA 4 Nose - 310 6 3 - - - M/71 GPA 24 Lung, eye, joints Nodules, ILD 1528 9 3 - - - F/64 MPA 24 Lung ILD 756 4 - 1003 0 - F/59 GPA 72 Lung Nodules 338 4 - - 0 - Figure 1. ROC curve and decision tree model Conclusion Our multicentre study demonstrated KL-6 as a reliable, non-invasive and easy-to-perform marker of ILD in AAV patients and its helpfulness for disease activity assessment. Changes in serum concentrations of KL-6 over time could be useful for monitoring AAV patients. Further study of KL-6 as a marker of response to therapy during long-term follow-up would also be worthwhile. Disclosure of Interests None declared